1. Field of the Invention
The present invention relates in general to a fluid-filled cylindrical elastic connector capable of reducing the amount of transmission of vibrations, based on flows of a fluid contained therein. More particularly, the invention is concerned with such a fluid-filled cylindrical elastic connector which is capable of effectively damping input vibrations having relatively low frequencies, and exhibiting a sufficiently low dynamic spring constant with respect to input vibrations having high frequencies.
2. Discussion of the Prior Art
There is known a cylindrical elastic connector such as a suspension bushing or engine mount used on a motor vehicle, which is interposed between two members in a vibration transmitting system for elastically or flexibly connecting these members in a vibration damping or isolating manner. Such a cylindrical elastic connector has an inner and an outer sleeve which are made of a metallic material and are disposed in radially spaced-apart relationship with each other. Between these inner and outer sleeves, there is interposed an elastic body such as a formed rubber mass, such that the two sleeves are elastically connected by the elastic body.
The elastic connector of the type indicated above is generally required to provide an excellent vibration damping effect with respect to low-frequency vibrations, and exhibit a sufficiently low dynamic spring rate or constant with respect to high-frequency vibrations. Conventionally, the elasticity or elastic deformation of the elastic body is primarily relied upon to meet these two requirements concerning the vibration damping and/or isolating characteristics. However, the conventional elastic connector suffers from considerable difficulty in meeting the requirements, particularly the requirement for providing a satisfactory effect of damping the low-frequency vibrations.
In view of the above drawback of the conventional cylindrical elastic connector, a so-called fluid-filled connector has been recently proposed, as disclosed in Publication Nos. 48-36151 and 52-16544 of examined Japanese Patent Applications. A fluid-filled cylindrical elastic connecter as disclosed in these publications has two fluid chambers which are partially defined by an elastic body and are filled with a suitable non-compressible fluid. The two fluid chambers are held in fluid communication with each other through a suitable orifice passage, so that the input vibrations having relatively low frequencies may be effectively damped by resonance of a fluid flowing through the orifice passage. The fluid flow is induced by relative pressure changes between the two fluid chambers due to elastic deformation of the elastic body upon application of the vibrations to the fluid-filled elastic connector.
In the fluid-filled elastic connector indicated above, the orifice passage for causing the fluid resonance is tuned so as to provide excellent damping characteristic for the vibrations having relatively low frequencies. However, the elastic connector also receives vibrations whose frequencies are higher than those of the excellently damped vibrations. When the frequency range of the vibrations received by the elastic connector is higher than the tuned frequency range of the orifice passage, substantially no flows of the fluid through the orifice passage occurs, or the orifice passage acts as if it were closed. In this case, therefore, the fluid-filled elastic connector exhibits a considerably high dynamic spring constant, and tends to undesirably suffer from deteriorated characteristics for isolating the high-frequency vibrations.